The thalamus, Hypothalamus, and pineal glands are part of a large structure called the diencephalon, which roughly translates to “interbrain.”
Hypothalamus is the middle-man between the nervous system and the endocrine system.
The thalamus is a major neural relay station from parts of the cerebrum to other parts of the cerebrum, from the cerebrum to the cerebellum, and from the cerebrum to the spinal cord and the rest of the soul. The thalamus also relays sensory signals from the body to the brain for processing. It’s also involved in gating and normalizing sensory input and motor output. The thalamus is also divided up into different nuclei, which play specific roles in what kinds of signals they relay.
For example, the ventral-posterior-lateral (VPL) nucleus relays sensory signals from the body below the head. In contrast, the ventral-posterior-medial (VPM) nucleus transmits the same signal from the head and face.
The Hypothalamus is the gateway from the nervous system to the endocrine system.
It’s involved in hormone production, circadian rhythm, and a variety of other autonomic functions such as body temperature, thirst, and hunger.
The pituitary is really two independent glands.
The anterior pituitary gland is mainly controlling by releasing and inhibiting hormones carried by a short plexus of blood vessels from the Hypothalamus.
Thalamus is the principal relay center in the forebrain, which receives sensory impulses from the spinal cord, brain stem, cerebellum, and other parts of the brain and direct them to appropriate areas of the cerebral cortex.
Functions of Hypothalamus:
A nice mnemonic of hypothalamus functions is the
4 Fs — food, fun, fever, and sex (“fucking”).
2. Control of the pituitary gland: Hypothalamus produces several hormones that stimulate or inhibit the secretion of pituitary hormones.
3. Regulation of emotional and behavioral patterns: Hypothalamus regulates feelings of rage, aggression, pain and pleasure, and the behavioral patterns related to sexual arousal.
4. Regulation of eating and drinking:
The feeding center is responsible for the hunger sensation. When sufficient food has been ingested, the satiety center inhibits the feeding center.
Thirst center is stimulated by the increased osmotic pressure of extracellular fluid. As a result, it causes a sensation of thirst. The intake of water restores the osmotic pressure to normal, relieving the thirst.
5. Control of body temperature:
On the off chance that the temperature of blood moving through the Hypothalamus is better than average, the Hypothalamus coordinates ANS to stimulate activities that promote heat loss. E.g., the vasodilatation of blood vessels of the body surface promotes heat loss.
Note: If the person is roaming in the sun in summers, the face becomes red due to the same reason.
If blood temperature is below normal, the Hypothalamus generates impulses that promote heat production and retention.
Note: In winters, blood vessels of body surfaces are constricted to prevent heat loss. This is because our skin becomes dry and undernourished during winters.
The pineal gland
The pineal gland, described by Descarte as the “seat of the soul,” is a small endocrine organ responsible for neurotransmitter production and maintenance of circadian rhythm. An interesting clinical correlate is that a pinealoma (a tumor of the pineal gland) produces an external manifestation such that mass effect from the tumor compresses a nearby structure, namely the superior colliculus. This leads to visual changes as the superior colliculus is a relay center for the optic nerve.
Melatonin may play a very important role in the regulation of 24–hours (diurnal) rhythm of our body. It is also called sleep-wake cycle or biological clock.
Melatonin also influences metabolism, pigmentation, menstrual cycle, as well as our defense capability.
What Happen If we completely remove Hypothalamus?
The hypothalamus’ primary role is to link the endocrine system (hormones) to the neural system via the pituitary gland. As such, it is related to systems such as hunger and thirst, body temperature and thermoregulation (sweating and blood flow), blood pressure, fatigue and circadian rhythms, but also, as part of the limbic system, to emotional behavior such as personal attachment (of parents, babies, and couples) and parenting behaviors, as well as learning and memory systems. It is also highly related to growth and sexual characteristics, as it plays an important part in the release of a growth-hormone-releasing hormone (i.e., the hormone that causes the release of other hormones that cause physical growth)
As to what would happen if it was completely removed, it’s difficult to know, but I imagine that complete removal would do serious and irreversible damage, that would probably lead to, at the very best, being bedridden and dependent on medical machinery for life, and in all likelihood to death. Hormones are essential for almost all of the processes of our body, and a complete loss of neural regulation of hormones would disrupt all bodily processes to an extreme degree.
Severe hypothalamic disorders, i.e., “only” severe dysfunction, rather than complete removal, can lead to problems regulating body temperature and blood pressure, which can lead to severe fatigue, loss of vision, heart problems, and muscle loss. It has also been linked to tumor growth. Less severe dysfunction can still lead to dizziness and weakness, hair loss, problems of bowel control, obesity, depression, osteoporosis, impotence, and more. Minor dysfunction can be treated with medical regulation of hormones. However, this is a lifelong disease that necessitates constant regulation of hormonal intake. In children, hypothalamic disorders can cause either over- or under-growth, and delayed or early onset of sexual maturity.
That being said, there are cases of people living with significant damage to their Hypothalamus, and surviving*, and sometimes managing to live relatively normal lives following significant relearning, and with lifelong hormonal problems that must be medicated. Exactly how much damage has been done is often difficult to tell in these cases, and they almost never specifically knock out the Hypothalamus, all of the Hypothalamus and nothing but the Hypothalamus.